Update keyring to 20.0.0

[pyup-bot]

This PR updates keyring from 19.3.0 to 20.0.0.

Changelog

20.0.0

------

* Extracted ``keyring.testing`` package to contain supporting
functionality for plugin backends. ``keyring.tests`` has been
removed from the package.

Links

• PyPI: https://pypi.org/project/keyring
• Changelog: https://pyup.io/changelogs/keyring/
• Repo: https://github.com/jaraco/keyring